Recent imaging apparatuses such as digital cameras have a focus detection function, and apparatuses with an autofocus (AF) function are widely used. The known focus detection methods include contrast AF and phase difference AF. In the contrast AF, a focal point at which a high-frequency component of an image signal peaks in intensity is detected. In the phase difference AF, two images with a phase difference horizontally (or vertically) occurring according to a degree of defocus are obtained, and the focal point is calculated based on the phase difference. Here, the phase difference is a distance between these images.
In the contrast AF, the peak in high-frequency component of an image signal is searched for while the focus lens is being moved. Thus, the contrast AF has a problem that it takes time to detect a focal point in the significant defocus state.
Here, PTL 1 discloses a conventional imaging apparatus (digital camera) that applies an image-plane phase difference AF using an image sensor for capturing main images, with the same principle as that of the phase difference AF that is used in single-lens reflex cameras. More specifically, one pixel of a solid-state imaging device (image sensor) includes a microlens and two light receiving units for a single color filter. One picture element consisting of pixels includes at least one pixel having a different arrangement of light receiving units. With the structure, the focal point can be detected using beams having different pupil dividing directions through an optical lens, and whether to add the output of light receiving units within one pixel or not can be selected. For example, in a structure where a signal can be output to the same frame within one pixel, first, the non-addition is selected to perform AF shooting with the image-plane phase difference detection. Then, the lens is focused based on information of the detection result, and addition is selected to capture the image for recording.